Science · Class 8 · Chapter 3

Health: The Ultimate Treasure

• Health — Complete physical, mental, and social well-being.
• Symptom / Sign — What's felt / what's seen or measured.
• Pathogen — A disease-causing organism.
• Communicable disease — Caused by a pathogen, spreads person to person.
• Non-communicable disease — Not caused by a pathogen; not contagious.
• Immunity — The body's natural ability to fight disease.
• Vaccine — Trains the immune system to fight a pathogen.
• Antibiotic resistance — Bacteria surviving despite antibiotic treatment.

Chapter 3 · Concept 1 of 10

What Does "Health" Really Mean?

• According to the WHO, health is a state of complete physical, mental, and social well-being — not merely the absence of disease.
• What a healthy person can do — Perform tasks efficiently, cope with difficult situations, and adjust well with peers and society.

Chapter 3 · Concept 2 of 10

How Can We Stay Healthy?

• Healthy habits — A balanced diet, staying active, enough sleep, yoga or pranayama, and avoiding tobacco, alcohol, and addictive drugs.
• A clean environment — Clean air and water matter too — the Air Quality Index (AQI) tells us how clean or polluted the air is. Emotional well-being, like time with friends and family, matters just as much.

Chapter 3 · Concept 3 of 10

Symptoms and Signs

• Symptom — What a person feels — like pain, dizziness, or tiredness.
• Sign — What can be seen or measured — like fever, a rash, or high blood pressure.

Chapter 3 · Concept 4 of 10

What Is a Disease?

• A disease affects the normal working of the body or mind — sometimes caused by pathogens, sometimes by poor nutrition or lifestyle.
• Pathogen — A disease-causing organism — bacteria, viruses, fungi, worms, or protozoa.

Chapter 3 · Concept 5 of 10

Communicable and Non-communicable Diseases

• | Cause | Spreads person to person? | Example
• Communicable — A pathogen — Yes — Typhoid, dengue, chickenpox
• Non-communicable — Lifestyle, diet, environment — No — Diabetes, asthma, cancer

Chapter 3 · Concept 6 of 10

How Diseases Spread

• Air — Coughing, sneezing — cold, flu, TB.
• Contact — Direct or indirect touch.
• Food & water — Contamination — typhoid, cholera.
• Vectors — Mosquitoes and other carriers — malaria, dengue.

Chapter 3 · Concept 7 of 10

Immunity and Vaccines

• Immunity — The body's natural ability to fight disease, carried out by the immune system.
• Vaccines — Train the immune system to recognise and attack a pathogen — giving acquired immunity. Vaccines are preventive, not curative.

Chapter 3 · Concept 8 of 10

Edward Jenner and Smallpox

• Jenner discovered that exposure to cowpox protected people against smallpox — leading to the world's first vaccine.
• An Indian tradition too — India historically used variolation, carried out by teekedaars, against smallpox even before modern vaccines existed.

Chapter 3 · Concept 9 of 10

Antibiotics

• Antibiotics are medicines that kill bacteria — they work only against bacterial infections, not viruses or protozoa.
• A lucky accident — Alexander Fleming discovered penicillin, the first antibiotic, in 1928 — after noticing a mould killing bacteria in a petri dish.

Chapter 3 · Concept 10 of 10

Antibiotic Resistance

• When medicine stops working — Bacteria that once died from an antibiotic can survive and multiply despite treatment — often from indiscriminate or incomplete use, including in animals. This makes infections harder to treat.

Quick Recap

Check Your Understanding

1. 1Group these as communicable or non-communicable: Cold and flu, Typhoid, Diabetes, Asthma, Chickenpox.
2. 2Identify the non-communicable diseases: (i) Typhoid (ii) Asthma (iii) Diabetes (iv) Measles.
3. 3There's a flu outbreak at school — several classmates are absent, some are coughing and sneezing. (i) What should the school do? (ii) How can you respond kindly to a sick benchmate? (iii) How can you protect yourself and others?